Liquid crystal panel substrate, liquid crystal panel, and electronic device and projection display device using the same

ABSTRACT

In a liquid crystal substrate in which a matrix of reflecting electrodes is formed on a substrate, a transistor is formed corresponding to each reflective electrode and a voltage is applied to the reflective electrode through the transistor. A silicon oxide film having a thickness of 500 to 2,000 angstroms is used as the passivation film and the thickness is set to a value in response to the wavelength of the incident light to maintain a substantially constant reflectance.

BACKGROUND OF THE INVENTION

[0001] 1. Field of Invention

[0002] The present invention relates to liquid crystal panels and liquidcrystal panels, and in particular, a technology suitable for activematrix liquid crystal panels in which pixel electrodes are switched withswitching elements formed on a semiconductor substrate or an insulatingsubstrate. The present invention also relates to an electronic deviceand a projection display device using the same.

[0003] 2. Description of Related Art

[0004] Liquid crystal panels having a structure in which a thin filmtransistor (TFT) array using amorphous silicon is formed on a glasssubstrate have been conventionally used as reflective active matrixliquid crystal panels which are used in light valves of projectiondisplay devices.

[0005] The active matrix liquid crystal panel using the TFT is atransmissive liquid crystal panel, and a pixel electrode is formed witha transparent conductive film. In transmissive liquid crystal panels,since the switching element-forming region, such as a TFT, which isprovided in each pixel is not a transparent region, it has a seriousdefect that the aperture ratio is low and decreases as the resolution ofthe panel is improved to XGA, or S-VGA.

[0006] As a liquid crystal panel having a smaller size than thetransmissive active matrix liquid crystal panel, a reflective activematrix liquid crystal panel in which pixel electrodes, as reflectingelectrodes, are switched with transistors formed on a semiconductorsubstrate or an insulating substrate has been proposed.

[0007] In such a reflective liquid crystal panel, the formation of apassivation film as a protective film on the substrate in which thereflecting electrodes are formed is often omitted since it is not alwaysnecessary. The present inventor has studied the formation of apassivation film on a reflective liquid crystal panel substrate.

[0008] In general, a silicon nitride film formed by a low pressure CVDprocess or a plasma CVD process is often used as a passivation film insemiconductor devices. The passivation film formed by a current CVDprocess inevitably has some variation of the thickness of approximately10%. Accordingly, the reflective liquid crystal panel has disadvantages,e.g. the reflectance noticeably varies with variation of the thicknessof the passivation film.

SUMMARY OF THE INVENTION

[0009] It is an object of the present invention to provide a reflectiveliquid crystal panel substrate and a liquid crystal panel having apassivation film which does not vary the refractive index of the liquidcrystal and having high reliability.

[0010] It is another object of the present invention to provide areflective liquid crystal panel having high reliability and excellentimage quality and an electronic device and projection display deviceusing the same.

[0011] The present invention for achieving the above object has a liquidcrystal panel substrate comprising a matrix of reflective electrodesformed on a substrate, a transistor formed corresponding to eachreflective electrode, a voltage applied to the reflective electrodesthrough the respective transistors, a passivation film formed on thereflecting electrodes, the passivation film having a thickness tocontrol a change in reflectance of the reflecting electrodes towavelengths of incident light to within approximately 1%, and thus thethickness is selected such that the variation of the thickness lessaffects the reflectance of the reflecting electrodes.

[0012] A phenomenon in which reflectance on the electrodes significantlyvaries with the wavelength of light can be suppressed by forming thepassivation film with a silicon oxide film.

[0013] A silicon oxide film having a thickness of 500 to 2,000 angstromsis used as the passivation film of the liquid crystal panel substrate.Although the silicon oxide film has a function as a protective filmslightly inferior to the silicon nitride film, it less affects thereflectance of the pixel electrode due to variation of the filmthickness compared to the silicon nitride film. Since a silicon oxidefilm having a thickness of 500 to 2,000 angstroms shows particularlyslight dependency of the reflectance on the wavelength, the use of thesilicon oxide film as the passivation film can reduce variation of thereflectance.

[0014] Further, the thickness of the passivation film is set to anadequate range in response to the wavelengths of incident light on eachreflecting electrode. In detail, the thickness of the silicon oxide filmas the passivation film is 900 to 1,200 angstroms for a pixel electrodereflecting blue light, 1,200 to 1,600 angstroms for a pixel electrodereflecting green light, or 1,300 to 1,900 angstroms for a pixelelectrode reflecting red light. When the thickness of the silicon oxidefilm as the passivation film is set to the above range, variation of thereflectance for each color can be suppressed to 1% or less, reliabilityof the liquid crystal panel is improved and the image quality isimproved in a projection display device using the reflecting liquidcrystal panel as a light valve.

[0015] It is preferred that the thickness of the silicon oxide film asthe passivation film be determined in consideration of the thickness ofan alignment film formed thereon. In this case, the alignment film has athickness of preferably 300 to 1,400 angstroms, and more preferably 800to 1,400 angstroms. Variation of the refractive index of the liquidcrystal can be effectively suppressed by setting the thickness of thealignment film to the above-mentioned range.

[0016] In a liquid crystal panel having a pixel region in which a matrixof pixel electrodes are disposed and peripheral circuits, such as ashift register and a control circuit, formed on the same substrate, apassivation film composed of a silicon oxide film may be formed abovethe pixel region and a passivation film composed of a silicon nitridefilm may be formed above the peripheral circuits. Since the thickness ofthe passivation film above the peripheral circuits does not affect thereflectance, the use of the silicon nitride film enables secureprotection of the peripheral circuits and improvement in reliability.

[0017] A silicon nitride film may be provided as an insulatinginterlayer between the reflecting electrodes and the metal layerthereunder, instead of the formation of the passivation film on thereflecting electrodes or by using together with the passivation filmcomposed of the silicon oxide film. The moisture resistance is therebyimproved and the MOSFET for pixel switching and the holding capacitorcan be prevented from corrosion due to water or the like.

[0018] A monolithic protective structure in which a silicon nitride filmformed on a passivation film of a silicon oxide is provided over theedge and the side wall of the laminate of the transistor for switchingthe pixel, and the insulating interlayer and metal layer which form awire region supplying a given voltage and signal to the transistor. Thewater proof property is thereby improved at the edge of the liquidcrystal panel in which water could otherwise readily penetrate, and thedurability is also improved since it acts as a reinforcing material.

[0019] When a liquid crystal panel using the above-mentioned liquidcrystal panel substrate is used in a light valve of a projection displaydevice, a color separation means for separating the light from a lightsource into three primaries, a first reflective liquid crystal panel formodulating red light from the color separation means, a secondreflective liquid crystal panel for modulating green light from thecolor separation means and a third reflective liquid crystal panel formodulating blue light from the color separation means are provided, thethickness of the silicon oxide film forming a passivation film of thefirst reflective liquid crystal panel is in a range of 1,300 to 1,900angstroms, the thickness of the silicon oxide film forming a passivationfilm of the second reflective liquid crystal panel is in a range of1,200 to 1,600 angstroms, and the thickness of the silicon oxide filmforming a passivation film of the third reflective liquid crystal panelis in a range of 900 to 1,200 angstroms, the passivation film has athickness in response to the wavelength of the color light to bemodulated in each light valve for modulating each color light. Variationof the reflectance and variation of the synthetic light thereforedecrease. Variation of hue of the color display in the projected lightbetween different projection display device products is prevented.

BRIEF DESCRIPTION OF THE DRAWINGS

[0020] FIGS. 1(a) and 1(b) is a cross-sectional view of a firstembodiment of a pixel region of a reflecting electrode side substrate ofa reflective liquid crystal panel in accordance with the presentinvention.

[0021]FIG. 2 is a cross-sectional view of an embodiment of a structureof a peripheral circuit of a reflecting electrode side substrate of areflective liquid crystal panel in accordance with the presentinvention.

[0022]FIG. 3 is a planar layout of a first embodiment of a pixel regionof a reflecting electrode side substrate of a reflective liquid crystalpanel in accordance with the present invention.

[0023]FIG. 4 is a cross-sectional view of an embodiment of an edgestructure of a reflecting electrode side substrate of a reflectiveliquid crystal panel in accordance with the present invention.

[0024]FIG. 5 is a cross-sectional view of another embodiment of areflecting electrode side substrate of a reflective liquid crystal panelin accordance with the present invention.

[0025]FIG. 6 is a plan view of an example of a layout of a reflectingelectrode side substrate of a reflective liquid crystal panel in anembodiment.

[0026]FIG. 7 is a cross-sectional view of an embodiment of a reflectiveliquid crystal panel using a liquid crystal panel substrate of anembodiment.

[0027]FIG. 8 is a graph including a gate driving waveform and a dataline driving waveform of a FET for pixel electrode switching of areflective liquid crystal panel in accordance with the presentinvention.

[0028]FIG. 9 is a block diagram of a video projector as an example ofprojection display devices in which a reflective liquid crystal panel ofan embodiment is used as a light valve.

[0029]FIG. 10 is a graph illustrating that the reflectance of areflecting electrode composed of an aluminum layer varies with thethickness of the silicon oxide film at a given length of the incidentlight.

[0030]FIG. 11 is a graph illustrating that the reflectance of areflecting electrode composed of an aluminum layer varies with thethickness of the silicon oxide film at a given length of the incidentlight.

[0031]FIG. 12 is a graph in which the reflectance is plotted at a givenwavelength interval when the thickness of the silicon oxide film ischanged within a wavelength range covering blue light.

[0032]FIG. 13 is a graph in which the reflectance is plotted at a givenwavelength interval when the thickness of the silicon oxide film ischanged within a wavelength range covering green light.

[0033]FIG. 14 is a graph in which the reflectance is plotted at a givenwavelength interval when the thickness of the silicon oxide film ischanged within a wavelength range covering red light.

[0034] FIGS. 15 (a), (b) and (c) are appearances of electronic devicesusing reflection liquid crystal panels in accordance with the presentinvention, respectively.

[0035]FIG. 16 is a cross-sectional view of another embodiment of areflecting electrode side substrate of a reflective liquid crystal panelin accordance with the present invention.

[0036]FIG. 17 is a cross-sectional view of another embodiment of areflecting electrode side substrate of a reflective liquid crystal panelin accordance with the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0037] Preferred embodiments in accordance with the present inventionwill now be described with reference to the drawings.

[0038] FIGS. 1(a), 1(b) and 3 show a first embodiment of a reflectingelectrode substrate of a reflective liquid crystal panel in accordancewith the present invention. FIGS. 1(a), 1(b) and 3 are a cross-sectionalview and a planar layout view, respectively, of one pixel section amonga matrix of pixels. FIG. 1(a) is a cross-sectional view taken alongcross-section line I-I of FIG. 3. FIG. 1(b) is a cross-sectional viewtaken along cross-section line II-II of FIG. 3. FIG. 6 is an entireplanar layout view of a reflecting electrode substrate of a reflectiveliquid crystal panel in accordance with the present invention.

[0039] In FIGS. 1(a) and 1(b), identification numeral 1 represents aP-type semiconductor substrate such as single-crystal silicon (or N-typesemiconductor substrate (N⁻⁻)), identification numeral 2 represents aP-type well region having an impurity content higher than that of thesemiconductor substrate formed on the surface of the semiconductorsubstrate 1, and identification numeral 3 represents a field oxide filmfor separating elements (so called LOCOS) formed on the surface of thesemiconductor substrate 1. The well region 2 is formed as a common wellregion of a pixel region in which a matrix of pixels of, for example,768 by 1,024 is provided, and is not limited to this. As shown in FIG.6, the well region 2 is separately formed from a well region in whichperipheral circuits, such as a data line driving circuit 21, a gate linedriving circuit 22, an input circuit 23 and a timing control circuit 24,which are disposed on the periphery of a pixel region 20 in which amatrix of pixels are arranged, are formed. The field oxide film 3 isformed into a thickness of 5,000 to 7,000 angstroms by selective thermaloxidation.

[0040] Two openings per pixel are formed in the field oxide film 3. Inthe center of one opening a gate electrode 4 a composed of polysiliconor metal silicide is formed through a gate oxide film (insulating film)4 b formed by thermal oxidation, source and drain regions 5 a and 5 bcomposed of N-type impurity doping layers (hereinafter referred to asdoping layers) are formed on the substrate surface at both sides of thegate electrode 4 a, and a MOSFET is thereby formed. The gate electrode 4a extends to the scanning direction (pixel line direction) to form agate line 4.

[0041] On the substrate surface in the other opening formed in the fieldoxide film 3, a P-type doping region 8 is formed. On the surface of theP-type doping region 8, an electrode 9 a composed of polysilicon ormetal silicide is formed through an insulating film 9 b formed bythermal oxidation. A capacitor for holding a voltage applied to thepixel is formed between the electrode 9 a and the P-type doping region 8through the insulating film 9. The electrode 9 a and the polysilicon ormetal silicide layer as the gate electrode 4 a of the MOSFET can beformed by the same process, and the insulating film 9 b under theelectrode 9 a and the insulating film as the gate insulating film 4 bcan be formed by the same process.

[0042] The insulating films 4 b and 9 b are formed on the semiconductorsubstrate surface in the openings by thermal oxidation into a thicknessof 400 to 800 angstroms. The electrodes 4 a and 9 a have a structure inwhich a poly-silicon layer having a thickness of 1,000 to 2,000angstroms is formed and a silicide layer of a high boiling point metalsuch as Mo or W having a thickness of 1,000 to 3,000 angstroms is formedthereon. The source and drain regions 5 a and 5 b are formed by means ofself-alignment by implanting an N-type impurity on the substrate surfaceat both sides of the gate electrode 4 a as a mask by ion implanting. Thewell region just below the gate electrode 4 a acts as the channel region5 c of the MOSFET.

[0043] The above-mentioned P-type doping region 8 is formed by, forexample, a doping treatment including exclusive ion implanting and heattreatment, and may be formed by ion implanting before the formation ofthe gate electrode. That is, after the insulating films 4 b and 9 b areformed, an impurity of the same conductivity type as the well isimplanted to form a region 8 on the well surface having a higherimpurity concentration and a lower resistance than those in the well.The concentration of impurities in the well region 2 is preferably1×10¹⁷/cm³ or less, and more preferably 1×10¹⁶/cm³ to 5×10¹⁶/cm³. Thepreferred concentration of the surface impurities in the source anddrain regions 5 a and 5 b is 1×10²⁰/cm³ to ×10²⁰/cm³. Also, theconcentration of the P-type doping region 8 is preferably 1×10¹⁸/cm³ to5×10¹⁹/cm³, and more preferably 1×10¹⁸/cm³ to 1×10¹⁹/cm³ in view ofreliability of the insulating film forming the holding capacitance andvoltage resistance.

[0044] A first insulating layer 6 is formed over the electrodes 4 a and9 a on the field oxide film 3, a data line 7 (refer to FIG. 3)substantially consisting of aluminum is formed on the insulating film 6,and a source electrode 7 a and an auxiliary bonding wire 10 are providedso as to protruded from the data line. The source electrode 7 a iselectrically connected to the source region 5 a through a contact hole 6a formed in the insulating film 6, one end of the auxiliary bonding wire10 is electrically connected to the drain region 5 b through a contacthole 6 b formed in the insulating film 6 and the other end iselectrically connected to the electrode 9 a through a contact hole 6 cformed in the insulating film 6.

[0045] The insulating film 6 is formed by, for example, depositing anHTO film (a silicon oxide film formed by a high temperature CVD process)having a thickness of approximately 1,000 angstroms and depositing aBPSG film (a silicate glass film containing boron and phosphorus) havinga thickness of approximately 8,000 to 10,000 angstroms. The metal layerwhich forms the source electrode 7 a (the data line 7) and the auxiliarybonding wire 10 has, for example, a four-layer structure ofTi/TiN/Al/TiN from the bottom. The thicknesses of the lower Ti layer,TiN layer, Al layer and upper Ti layer are 100 to 600 angstroms,approximately 1,000 angstroms, 4,000 to 10,000 angstroms and 300 to 600angstroms, respectively.

[0046] A second insulating interlayer 11 is formed over the sourceelectrode 7 a, the auxiliary bonding wire 10 and the insulatinginterlayer 6, and a light shielding film comprising a second metal layer12 composed of aluminum is formed on the second insulating interlayer11. The second metal layer 12 as the light shielding film is formed as ametal layer for forming bonding wires between devices in the peripheralcircuits, such as a driving circuit, which are formed on the peripheryof the pixel region, as described below. No additional step is thereforerequired for forming only the light shielding film 12, and the processcan be simplified. The light shielding film 12 is formed so as to coverthe entire pixel region 20 and has an opening 12 a on the auxiliarybonding wire 10 for piercing a pillar connecting plug 15 whichelectrically connects a pixel electrode with a MOSFET described later.That is, in the plan view shown in FIG. 3, a rectangular frame 12 arepresents the above-mentioned opening and the entire outside of theopening 12 a is covered with the light shielding film 12. The incidentlight from the upper side in FIG. 1 (the liquid crystal layer side) isalmost completely shielded and a light leakage current flow due to lighttransmission in the channel region 5 c and the well region 2 of theMOSFET for pixel switching can be prevented.

[0047] The second insulating layer 11 is formed by, for example,depositing a silicon oxide film by a plasma CVD process using TEOS(tetraethylorthosilicate) (herein after referred to as a TEOS film) intoa thickness of approximately 3,000 to 6,000 angstroms, depositing a SOGfilm (a spin-on-glass film), etching it by an etch-back process, anddepositing a second TEOS film thereon into a thickness of approximately2,000 to 5,000 angstroms. The second metal layer 12 as the lightshielding film may have the same structure as the first metal layers 7(7 a) and 10, and may have, for example, a four layer structure ofTi/TiN/Al/TiN from the bottom. The thicknesses of the lower Ti layer,TiN layer, Al layer and upper Ti layer are 100 to 600 angstroms,approximately 1,000 angstroms, 4,000 to 10,000 angstroms and 300 to 600angstroms, respectively.

[0048] In this embodiment, a third insulating layer 13 is formed on thelight shielding layer 12, and a rectangular pixel electrode 14 as areflective electrode almost corresponding to one pixel is formed on thethird insulating layer 13 as shown in FIG. 3. A contact hole 16 isprovided inside the opening 12 in the light shielding film 12 so as topierce the third insulating interlayer 13 and the second insulatinginterlayer 11, and the contact hole 16 is filled with a pillarconnecting plug 15 composed of a high melting point metal, such astungsten, which electrically connects the auxiliary bonding wire 10 andthe pixel electrode 14. A passivation film 17 is formed on the entirepixel electrode 14.

[0049] When forming a liquid crystal panel, an alignment film is formedon a substrate at the reflective electrode side, an opposing substratewhich is provided with an opposing (common) electrode therein and analignment film thereon is provided on the inside face at a given gap soas to face the substrate, and a liquid crystal is encapsulated into thegap.

[0050] For example, after tungsten is deposited by a CVD process to formthe connecting plug 15, the tungsten and the third insulating interlayer13 are planarized by a chemical mechanical polishing (CMP) process, thepixel electrode 14 is formed by a low temperature sputtering processusing aluminum into a thickness of 300 to 5,000 angstroms and is formedby a patterning process into a square having a side of approximately 15to 20 μm. The connecting plug 15 may be formed by smoothing the thirdinsulating interlayer 13 by a CMP process, providing the contact holeand depositing tungsten therein. The passivation film 17 is composed ofa silicon oxide film having a thickness of 500 to 2,000 angstroms in thepixel region and a silicon nitride film having a thickness of 2,000 to10,000 angstroms in the scribe section. A seal section represents aregion which is formed by a sealing material for fixing the gap betweenthe two substrates in the liquid crystal. The scribe section representsa section along a scribe region, i.e., the edge of the liquid crystalpanel substrate, when a number of reflective liquid crystal panelsubstrates are formed in a semiconductor wafer and separated alongscribe lines into semiconductor chips.

[0051] The use of a silicon oxide film as the passivation film 17covering the pixel region can prevent a significant change in areflectance due to the variation of the film thickness and thewavelength of the light.

[0052] On the other hand, the passivation film 17 covering a regionoutside the region in which the liquid crystal is encapsulated (outsidethe seal section) is formed of a single-layer structure consisting of asilicon nitride film or a double-layer structure consisting of a siliconoxide film and a silicon nitride film thereon in order to furtherimprove reliability, in which the silicon nitride film is superior tothe silicon oxide film in terms of water proof property. Although watercan readily penetrate from the peripheral region of the substratecontacting to the outer atmosphere and in particular the scribe section,the silicon nitride protective film covering the region can furtherimprove the reliability and durability at the region.

[0053] A polyimide alignment film is formed on the entire passivationfilm 17 and subjected to rubbing treatment to form a liquid crystalpanel.

[0054] The thickness of the passivation film 17 can be determined withinan adequate range in response to the wavelength of the incident light.The thickness of the silicon oxide as the passivation film is in a rangeof 900 to 1,200 angstroms for a pixel electrode reflecting blue light,1,200 to 1,600 angstroms for a pixel electrode reflecting green light,or 1,300 to 1,900 angstroms for a pixel electrode reflecting red light.A thickness of the silicon oxide film as the passivation film set towithin the range can suppress the variation of the reflectance in thereflective electrode composed of aluminum to 1% or less. The ground isillustrated below.

[0055]FIGS. 10 and 11 show the results of dependency of the reflectanceof the aluminum reflective electrode on the thickness of the siliconoxide film at different wavelengths. In FIG. 10, symbol ⋄ representsreflectance at a thickness of 500 angstroms, symbol □ representsreflectance at a thickness of 1,000 angstroms, symbol Δ representsreflectance at a thickness of 1,500 angstroms, and symbol x representsreflectance at a thickness of 2,000 angstroms. In FIG. 11, symbol ⋄represents reflectance at a thickness of 1,000 angstroms, symbol □represents reflectance at a thickness of 2,000 angstroms, symbol Δrepresents reflectance at a thickness of 4,000 angstroms, and symbol xrepresents reflectance at a thickness of 8,000 angstroms.

[0056] As shown in FIG. 11, at a thickness of 4,000 angstroms thereflectance decreases approximately 3% from 0.89 to 0.86 as thewavelength changes from 450 nm to 550 nm and the reflectance decreasesapproximately 8% from 0.85 to 0.77 as the wavelength changes from 700 nmto 800 nm. At a thickness of 8,000 angstroms the reflectance decreasesapproximately 3% from 0.89 to 0.86 as the wavelength changes from 500 nmto 600 nm and the reflectance decreases approximately 6% from 0.86 to0.80 as the wavelength changes from 650 nm to 750 nm. In contrast, nosignificant changes are observed at a thickness of 500 angstroms, 1,000angstroms, 1,500 angstroms or 2,000 angstroms. These results illustratethat the effective thickness of the silicon oxide film is in a range of500 to 2,000 angstroms.

[0057] As a result, a reflective liquid crystal panel having a reduceddependency of the reflectance on the wavelength can be achieved by athickness of 500 to 2,000 angstroms as the passivation film formed onthe reflective electrode.

[0058]FIGS. 10 and 11 also demonstrate that the reflectance slightlychanges in a specified thickness range of the silicon oxide film. Thepresent inventor further studied an optimum thickness range of thesilicon oxide film for the incident and reflecting color light. Theresults are shown in FIGS. 12 to 14. FIG. 12 is a graph illustratingreflectances at various thicknesses of the silicon oxide film in awavelength range of 420 to 520 nm for blue light and its neighbor, FIG.13 is a graph illustrating reflectances at various thicknesses of thesilicon oxide film in a wavelength range of 500 to 600 nm for greenlight and its neighbor, and FIG. 14 is a graph illustrating reflectancesat various thicknesses of the silicon oxide film in a wavelength rangeof 560 to 660 nm for red light and its neighbor.

[0059]FIG. 12 demonstrates that at a thickness of 800 angstroms thereflectance decreases by approximately 1.1% from 0.896 to 0.882 as thewavelength changes from 440 nm to 500 nm. At a thickness of 1,300angstroms, the reflectance changes by approximately 0.6% from 0.887 to0.893 as the wavelength changes from 420 nm to 470 nm and thereflectance is noticeably lower than those at other thicknesses within awavelength of 420 to 450 nm. In contrast, no significant changes inreflectance are observed and a satisfactorily high reflectance isachieved at a thickness of 900 angstroms, 1,000 angstroms, 1,100angstroms or 1,200 angstroms.

[0060] As shown in FIG. 13, at a thickness of 1,100 angstroms thereflectance decreases by approximately 1.6% from 0.882 to 0.866 as thewavelength changes from 550 nm to 600 nm. At a thickness of 1,700angstroms the reflectance is considerably lower than those at otherthicknesses within a wavelength of 500 nm to 530 nm. In contrast, nosignificant changes in reflectance are observed and a satisfactorilyhigh reflectance is achieved at a thickness of 1,250 angstroms, 1,400angstroms or 1,550 angstroms.

[0061] As shown in FIG. 14, at a thickness of 1,200 angstroms thereflectance decreases by approximately 3.4% from 0.882 to 0.848 as thewavelength changes from 560 nm to 660 nm. At a thickness of 2,000angstroms the reflectance is considerably lower than at otherthicknesses within a wavelength of 560 nm to 610 nm. In contrast, nosignificant changes in reflectance are observed and a satisfactorilyhigh reflectance is achieved at a thickness of 1,400 angstroms, 1,600angstroms or 1,800 angstroms.

[0062] FIGS. 12 to 14 demonstrate that when a thickness of the siliconoxide film as the passivation film is set to within the range of 900 to1,200 angstroms for a pixel electrode which reflects blue light, 1,200to 1,600 angstroms for a pixel electrode which reflects green light or1,300 to 1,900 angstroms for a pixel electrode which reflects red light,the variation of the reflectance for each color can be suppressed to 1%or less and a satisfactorily high reflectance can be achieved.

[0063] Each of the graphs shown in FIGS. 12 to 14 shows the reflectancewhen a polyimide alignment film is formed with a thickness of 1,100angstroms on the passivation film. The optimum thickness range of thesilicon oxide film slightly shifts with a different thickness of thealignment film. Regarding the thickness range of the alignment film, itis not capable of aligning if its thickness is less than 300 angstromsin view of suppressing the variation of reflectance, whereas thepolyimide absorbs high wavelength light and low wavelength light and hasappreciable capacitance which is connected in series to the liquidcrystal capacitor in the equivalent circuit; therefore it is preferredthat the thickness of the alignment film be within a range of 300 to1,400 angstroms. If a decrease in the alignment capability due to adecreased thickness of the alignment film is anticipated, the thicknessis preferably in a range of 800 to 1,400 angstroms.

[0064] When the thickness of the alignment film is within theabove-mentioned range and the thickness of the silicon oxide film in theliquid crystal panel for each color is within the above-mentioned range,the variation of the reflectance can be satisfactorily suppressed to 1%or less.

[0065] Accordingly, when a color display is formed in one liquid crystalpanel, the thickness of the passivation film on the reflective electrodecan be varied according to the color of each pixel. That is, in aconfiguration where an RGB color filter is formed on the inner face ofthe opposing substrate facing the reflective substrate in response topixel electrodes and the color light passing through the color filter isreflected from the pixel electrode, a single plate-type reflectiveliquid crystal panel having high reflectance can be obtained by settingthe thickness of the passivation film formed on the pixel electrodereflecting red light from the red (R) color filter to 1,300 to 1,900angstroms, the thickness of the passivation film formed on the pixelelectrode reflecting green light from the green (G) color filter to1,200 to 1,600 angstroms and the thickness of the passivation filmformed on the pixel electrode reflecting blue light from the blue (B)color filter to 900 to 1,200 angstroms. The liquid crystal panel canalso be used as a light valve for a single plate-type projection displaydevice. The color light may be formed by a means which converts lightincident on each pixel electrode into the color light, for example, adichroic mirror, instead of the color filter.

[0066] The liquid crystal panel in accordance with the present inventioncan also be used in a projection display device described later which isprovided with a liquid crystal panel reflecting red light, a liquidcrystal panel reflecting green light and a liquid crystal panelreflecting blue light. In this case, it is preferred that thethicknesses of the silicon oxide film as the passivation film be in arange of 1,300 to 1,900 angstroms for the liquid crystal panel in thelight valve for modulating red light, in a range of 1,200 to 1,600angstroms for the liquid crystal panel in the light valve for modulatinggreen light, and in a range of 900 to 1,200 angstroms for the liquidcrystal panel in the light valve for modulating blue light,respectively.

[0067]FIG. 3 is a planar layout view of the liquid crystal substrate atthe reflection side shown in FIG. 1. As shown in FIG. 3, the data line 7and the gate line 4 are formed so as to cross each other in thisembodiment. Since the gate line 4 is formed so as to act as the gateelectrode 4 a, the hatched region H of the gate line 4 in FIG. 3 acts asthe gate electrode 4 a and a channel region 5 c of MOSFET for pixelswitching is provided on the substrate surface thereunder. The sourceand drain regions 5 a and 5 b are formed on the substrate surface atboth sides (at the upper and lower sides in FIG. 3) of the channelregion 5 c. The source electrode 7 a connecting to the data line isformed so as to protrude from the data line 7, extended along thevertical direction in FIG. 3, and is connected to the source region 5 aof the MOSFET through the contact hole 6 b.

[0068] The P-type doping region as a constituent of one terminal of theholding capacitor is formed so as to link to the P-type doping region inthe adjacent pixel in the direction parallel to the gate line 4 (thepixel line direction). It is connected to a power line 70 providedoutside the pixel region through contact holes 71 so that a givenvoltage V_(SS), such as 0 volt (ground voltage), is applied. The givenvoltage V_(SS) may be close to a voltage of the common electrodeprovided on the opposing substrate, a central voltage of the amplitudeof image signals supplied to close to the data line, or an intermediatevoltage between the common electrode voltage and the amplitude centralvoltage of the image signals.

[0069] The connection of the P-type doping region 8 to the voltageV_(SS) at the outside of the pixel region stabilizes the voltage of oneelectrode of the holding capacitor and the holding voltage held in theholding capacitor during the non-selection time period of the pixel (thenon-leading time of the MOSFET), and decreases the variation of thevoltage applied to the pixel electrode during one frame time period.Since the P-type doping region 8 is provided near the MOSFET and thevoltage of the P-type well is simultaneously fixed, the substratevoltage of the MOSFET is stabilized and the variation of a thresholdvoltage due to the back gate effect can be prevented.

[0070] Although not shown in the drawings, the power line 70 is alsoused as a line which supplies a given voltage V_(SS) as a well voltageto the P-type well region (separated from the well of the pixel region)in the peripheral circuit provided outside the pixel region. The powerline 70 is formed of the first metal layer which is the same as the dataline 7.

[0071] Each pixel electrode 14 has a rectangular shape and is providedin close proximity to the adjacent pixel electrode 14 at a givendistance, for example, 1 μm, so as to decrease the light leaked betweenthe pixel electrodes as much as possible. Although the center of thepixel electrode is shifted from the center of the contact hole in thedrawings, it is preferable that both centers substantially agree witheach other due to the following reason. Since the second metal layer 12having a light shielding effect has an opening 12 a at the periphery ofthe contact hole 16, the opening 12 a provided near the edge of thepixel electrode 14 causes random reflection between the second metallayer 12 and the back surface of the pixel electrode of the lightincident from the gap between the pixel electrodes in which the lightreaches the opening 12 a and leaks from the opening through the lowersubstrate. It is therefore preferable that the center of the pixelelectrode and the center of the contact hole 16 substantially agree witheach other, because the distance in which the light incident from thegap with the adjacent pixel reaches the contact hole is almost equalizedat the edge of each pixel electrode and the light barely reaches thecontact hole which will form the light incident on the substrate side.

[0072] Although the above-mentioned embodiment includes theN-channel-type MOSFET for pixel switching and the P-type doping layer ofsemiconductor region 8 as one electrode of the holding capacitance, anN-type well region 2, a P-channel-type MOSFET for pixel switching and aN-type doping layer of semiconductor region as one electrode of theholding capacitance are also available. In this case, it is preferablethat a given voltage V_(DD) is applied to the N-type doping layer as oneelectrode of the holding capacitance as in the P-type well region. It ispreferred that the given voltage V_(DD) be a higher voltage of the powervoltages since it applies a voltage to the N-type well region. Forexample, when a voltage of image signals applied to the source and drainin the MOSFET for pixel switching is 5 volts, it is preferable that thegiven voltage V_(DD) also be 5 volts.

[0073] A high voltage, e.g. 15 volts, is applied to the gate electrode 4a of the MOSFET for pixel switching, whereas logic circuits, such as ashift resistor, in the peripheral circuit, are driven by a low voltage,e.g. 5 volts (but a part of the peripheral circuit, for example acircuit for applying a scanning signal to the gate line is driven at 15volts). It is conceivable that the thickness of a gate insulating filmin a FET as a peripheral circuit which is driven at 5 volts is lowerthan that of a gate insulating film of an FET for pixel switching (byforming the gate insulating film by another process or by etching thesurface of the gate insulating film of the FET in the peripheralcircuit) in order to improve the response of the FET in the peripheralcircuit and increase the operation rate of the peripheral circuit (inparticular, a shift resistor in a driving circuit at the data line siderequiring high speed scanning) . When such a technology is applied, thethickness of the gate insulating film of the FET as a constituent of theperipheral circuit can be reduced to approximately one third to onefifth the thickness of the gate insulating film of the FET for pixelswitching (for example, 80 to 200 angstroms) in view of voltageresistance.

[0074] The driving waveform in the first embodiment has a shape as shownin FIG. 8. In the drawing, V_(G) represents scanning signals applied tothe gate electrode of the MOSFET for pixel switching, the time periodt_(1H) represents a selection time period (scanning time period) to leadthe MOSFET of the pixel and the time period other than that is anon-selection time period so as not to lead MOSFET of the pixel.Further, V_(d) represents the maximum amplitude of the image signalsapplied to the data line, V_(c) represents a central voltage of theimage signals, and LC-COM represents a common voltage applied to theopposing (common) electrode formed on the opposing substrate facing thereflective electrode substrate.

[0075] The voltage applied between the electrodes of the holdingcapacitor is determined by the difference between the image signalvoltage V_(d) applied to the data line as shown in FIG. 8 and a givenvoltage V_(SS), such as 0 volts, applied to the P-type semiconductorregion 8. The difference between the image signal voltage V_(d) and thecentral voltage V_(C) of the image signal, i.e., approximately 5 volts,is, however, sufficient for the voltage difference which is to beapplied to the holding capacitor (the common voltage LC-COM applied tothe opposing (common) electrode 33 provided on the opposing substrate ofthe liquid crystal panel in FIG. 6 is shifted by ΔV from V_(c), whereasthe voltage actually applied to the pixel electrode is also shifted byΔV and becomes V_(d)-ΔV. The first embodiment therefore permits that thedoping region 8 forming one terminal of the holding capacitor is set tobe reverse polarity to the well (N-type for the P-type well) and it isconnected to a voltage of near V_(c) or LC-COM at the periphery of thepixel region so as to hold a voltage different from the well voltage(for example, V_(SS) for the P-type well) . By simultaneously formingthe insulating film 9 b just below the polysilicon or metal silicidelayer as one electrode 9 a of the holding capacitor with the gateinsulating film of the FET forming a peripheral circuit, not the gateinsulating film of the FET for pixel switching, the thickness of theinsulating film in the holding capacitor can be reduced to one third toone fifth compared to the above-mentioned embodiment and the capacitancecan be increased by three to five times.

[0076]FIG. 1(b) is a cross-sectional view (cross-section II-II in FIG.3) of the periphery of the pixel region in the first embodiment inaccordance with the present invention. The drawing shows a configurationof a section in which the doping region 8 extending in the scanningdirection of the pixel region (pixel line direction) is connected to agiven voltage (V_(SS)). Identification number 80 represents a P-typecontact region which is formed by the same step as the source/drainregion of the MOSFET in the peripheral circuit, in which impuritieshaving the same conductivity type are ion-implanted after the formationof the gate electrode into the doping region 8 which is formed beforethe formation of the gate electrode. The contact region 80 is connectedto the line 70 through the contact hole 71 to apply a constant voltageV_(SS). The upper face of the contact region 80 is also shielded with alight shielding film 14′ composed of a third metal layer.

[0077]FIG. 2 is a cross-sectional view of an embodiment of a CMOScircuit device forming a peripheral circuit, e.g. a driving circuit,outside the pixel region. In FIG. 2, the positions having the samenumbers as FIG. 1 represent the metal layer, insulating film andsemiconductor region which are formed by the same step.

[0078] In FIG. 2, identification numbers 4 a and 4 a′ represent gateelectrodes of an N-channel MOSFET and a P-channel MOSFET forming aperipheral circuit (CMOS circuit) such as a driving circuit,respectively, identification numbers 5 a (5 b) and 5 a′ (5 b′) representan N-type doping region and a P-type doping region, respectively, astheir respective source and drain regions, and identification numbers 5c and 5 c′ represent their respective channel regions. The contactregion 80 for supplying a constant voltage V_(SS) to the P-type dopingregion 8 as one electrode of the holding capacitor in FIG. 1 is formedby the same step as the P-type doping region 5 a′ (5 b′) as the source(drain) region of the P-channel MOSFET. Identification numbers 27 a and27 c represent source electrodes formed by the first metal layer andconnected to the power voltage (any one of 0 volt, 5 volts and 15volts), and identification number 27 b represents a drain electrodeformed by the first metal layer. Identification number 32 a represents awiring layer composed of the second metal layer and is used as a wirefor connecting between the devices forming a peripheral circuit.Identification number 32 b also represents a power wiring layer composedof the second metal layer and acts as a light shielding film. The lightshielding film 32 b can be connected to any one of V_(c), LC-COM, powervoltage, a constant voltage, e.g. 0 volt, and a variable voltage. Theshielding film formed from the same layer as the wiring layers 32 a and32 b may be in a floating voltage (non-applied voltage) state byseparating with the wiring layers 32 a and 32 b. Identification number14′ represents a third metal layer which is used as a light shieldingfilm in the peripheral circuit and prevents erroneous operation of theperipheral circuit due to unstable voltage in the semiconductor regionwhich is caused by carriers formed during light transmittance in thesemiconductor region of the peripheral circuit. Accordingly, theperipheral circuit is also shielded from light by the second and thirdmetal layers.

[0079] As described above, the passivation film 17 in the peripheralcircuit may be a protective film composed of a silicon nitride film or adouble-layered film of silicon oxide and silicon nitride thereon, inwhich the silicon nitride protective film is superior to the siliconoxide film as the passivation film in the pixel region. The source/drainregion of the MOSFET forming the peripheral circuit of this embodimentmay be formed by a self-alignment process, although it not limited tothis. The source/drain region of each MOSFET may have a LDD (lightlydoped drain) structure or a DDD (double doped drain) structure. It ispreferred that the FET for pixel switching have an offset structure inwhich the gate electrode is distant from the source/drain region, takinginto consideration that the FET for pixel switching is driven by a highvoltage and the leakage current must be prevented.

[0080]FIG. 4 shows a preferred embodiment of an edge structure of areflecting electrode (pixel electrode) substrate. In FIG. 4, the partshaving the same identification numbers represent the layers andsemiconductor regions formed by the same steps.

[0081] As shown in FIG. 4, the edge of the laminate composed of theinsulating interlayer and the metal layer and its side wall has amonolithic protective structure in which a silicon nitride film 18 isformed on the silicon oxide passivation film 17 which covers the pixelregion and the peripheral circuit. The edge corresponds to each of theedges of substrates (semiconductor chip) which are formed on a siliconwafer and separated by dicing along the scribe lines. The lower rightportion of the step in FIG. 4 corresponds to the scribe region.

[0082] Since the upper section and side wall of the substrate arecovered with the silicon nitride protective film at the edge, water andthe like will barely penetrate from the edge, durability is improved andthe yield is improved due to reinforcement of the edge. In thisembodiment, a sealing material 36 for encapsulating the liquid crystalis provided on the monolithic protective structure which is perfectlyplanarized. The distance to the opposing substrate therefore can bemaintained constant regardless of variation of the thickness whether theinsulating interlayer and the metal layer are present or not. Since theabove configuration permits a single-layered silicon oxide protectivefilm on the reflecting electrode forming a pixel electrode, it cansuppress a decrease in reflectance and dependence of the reflectance onthe wavelength.

[0083] As shown in FIG. 4, in this embodiment, the third metal layer 14′is the same as the layer 14 which is used as the light shielding film inthe peripheral circuit region and the reflection electrode of the pixel,and it is connected to the predetermined voltage through the second andfirst metal layers 12′ and 7′ and fixed to the substrate voltage. Alsothe second metal layer 12′ or the first metal layer 7′ may be extendedunder the sealing material 36 instead of the third metal layer 14′ to beused as a layer for fixing the voltage. This is capable of preventingstatic electricity during the formation of the liquid crystal substrateand liquid crystal panel and after the formation of the liquid crystalpanel.

[0084]FIG. 5 shows another embodiment in accordance with the presentinvention. FIG. 5 is a cross-sectional view along line I-I in the planarlayout in FIG. 3, as in FIG. 1. In FIG. 5, the sections having the sameidentification numbers as FIGS. 1 and 2 represent the layers and thesemiconductor regions formed by a similar process to the embodimentshown in these drawings. In this embodiment, a silicon nitride film 13 bis formed under the insulating interlayer 13 a composed of the TEOS film(partly including a remaining SOG film during etching) between thereflecting electrode 14 and the light shielding layer 12 thereunder.Alternatively, a silicon nitride film 13 b may be formed on the TEOSfilm 13 a. The use of a configuration having an additional siliconnitride film inhibits penetration of water and thus improves moistureresistance.

[0085] The thickness of the passivation film on the reflecting electrodeis similar to the embodiment shown in FIG. 1.

[0086]FIG. 16 shows another embodiment in accordance with the presentinvention. FIG. 16 is a cross-sectional view along line I-I in theplanar layout in FIG. 3, as in FIG. 1. In FIG. 16, the sections havingthe same identification numbers as FIGS. 1 and 2 represent the layersand the semiconductor regions formed by a similar process to theembodiment shown in those drawings. In this embodiment, a siliconnitride film 13 b is formed on the insulating interlayer 13 a composedof the TEOS film (partly including a remaining SOG film during etching)between the reflecting electrode 14 and the metal layer thereunder asthe shielding layer 12. The silicon nitride film 13 a can be planarizedby a CMP process or the like. The formation of the silicon nitride filmdecreases openings in the silicon nitride section compared to theembodiment in FIG. 5, and prevents penetration of water, resulting infurther improvement in moisture resistance. The space between thereflecting electrode and the adjacent electrode is formed of aprotective insulating film 17 and the silicon nitride film 13 b. Sincethe refractive index of the silicon nitride is 1.9 to 2.2 and higherthan the refractive index 1.4 to 1.6 of the silicon oxide used in theprotective insulating film 17, the incident light on the protectiveinsulating film 17 from the liquid crystal side is reflected at theinterface with the silicon nitride film 13 b because of the differenceof the refractive indices. Since the light incident on the interlayer isdecreased, unstable voltage in the semiconductor region caused bycarriers which are formed by light transmittance in the semiconductorregion are prevented.

[0087] In this embodiment, the silicon nitride film 13 b may be formedafter planarization of the insulating interlayer 13 a composed of theTEOS film by a CMP process or the like. In general, a film having athickness of 8,000 to 12,000 angstroms which corresponds to local stepsmust be deposited by, for example, a CMP process in order to offset thelocal steps. The silicon nitride film used in 13 b generally causes ahigh stress on the lower film as its thickness increases. In thisembodiment, since the insulating interlayer 13 a is planarized bypolishing by means of a CMP process and the silicon nitride film 13 b isformed thereon, the thickness of the silicon nitride film 13 b depositedby a CMP process or the like can be reduced, and thus the stress of thesilicon nitride film 13 b is reduced. Since the space between thereflecting electrode 14 and the adjacent reflecting electrode iscomposed of the protective insulating film 17 and silicon nitride film13 b in this case, the light incident on the interlayer decreases, andunstable voltage in the semiconductor region due to carriers formed bylight transmittance in the semiconductor region is prevented. It ispreferable in this embodiment that the thickness of the silicon nitridebe 2,000 to 5,000 angstroms. A thickness of 2,000 angstroms or moreimproves moisture resistance of the silicon nitride film 13 b, whereas athickness of 5,000 angstroms or less decreases the etching depth of thecontact hole 16, permits ready etching and relaxes the stress on thelower film.

[0088] The thickness of the passivation film on the reflecting electrodeis the same as the embodiment in FIG. 1.

[0089]FIG. 6 is a planar layout of an entire liquid crystal panelsubstrate (reflection electrode substrate) in which the above-mentionedembodiment is applied.

[0090] As shown in FIG. 6, in this embodiment a light shielding film 25is provided in order to shield the light incident on the peripheralcircuits provided on the periphery of the substrate. The peripheralcircuits are provided on the periphery of the pixel region 20 in which amatrix of the pixel electrodes is disposed, and include a data linedriving circuit 21 for supplying image signals to the data line 7 inresponse to the image data, a gate line driving circuit 22 forsequentially scanning gate lines 4, an input circuit for reading theimage data from the outside through the pad region 26, and a timingcontrol circuit 24 for controlling these circuits. These circuits areformed by combining active devices or switching devices composed ofMOSFETs formed by the same step as or a different step to the MOSFET forswitching the pixel electrodes and loading devices, such as resistorsand capacitors.

[0091] In this embodiment, the light shielding film 25 is composed ofthe third metal layer which is formed by the same step as the pixelelectrode 14 shown in FIG. 1 so as to apply a given voltage, e.g. apower voltage, the central voltage V_(c) of the image signal or a commonvoltage LC-COM. Application of the given voltage to the light shieldingfilm 25 can reduce reflection compared to a floating voltage and othervoltages. The light shielding film 25 may be in a floating voltage(non-applied voltage) state so that the light shielding film 25 will notapply a voltage to the liquid crystal 37. Reference numeral 26represents a pad used for supplying the power voltage or a pad regionprovided with a terminal.

[0092]FIG. 7 is a cross-sectional view of a reflection liquid crystalpanel using the above-mentioned liquid crystal panel substrate 31. Asshown in FIG. 7, a supporting substrate 32 composed of glass or ceramicis bonded to the back surface of the liquid crystal panel substrate 31with a bonding agent. A glass substrate 35 at the incident side having acounter electrode (common electrode) composed of a transparent electrode(ITO) for applying a common voltage LC-COM is opposed to the frontsurface of the liquid crystal panel substrate 31 at an adequatedistance, and a well known TN (twisted nematic) liquid crystal or a SH(super homeotropic) liquid crystal 37 in which the liquid crystalmolecules are substantially vertically aligned in a non-voltage appliedstate is encapsulated into a gap formed by sealing the periphery of thesubstrates with a sealing material 36 to form a liquid crystal panel 30.The position of the sealing material is determined so that the padregion 26 is present outside the sealing material 36.

[0093] The light shielding film 25 on the peripheral circuits face thecounter electrode 33 through the liquid crystal 37. Since the LC commonvoltage is applied to the counter electrode 33 when the LC commonvoltage is applied to the light shielding film 25, no direct currentvoltages are applied to the liquid crystal disposed therebetween. As aresult, liquid crystal molecules are always twisted by approximately 90degrees in the TN liquid crystal or always vertically aligned in the SHliquid crystal.

[0094] In this embodiment, since the liquid crystal panel substrate 31composed of the semiconductor substrate is bonded to the supportingsubstrate 32 composed of glass or ceramic at the back surface with abonding agent, the strength is significantly enhanced. As a result, whenthese are bonded to the opposing substrate after the supportingsubstrate 32 is bonded to the liquid crystal panel substrate 31, the gapof the liquid crystal layer is equalized over the entire panel.

[0095] The above description includes a configuration of a reflectiveliquid crystal panel substrate using a semiconductor substrate and aliquid crystal panel using the same. A configuration of a reflectiveliquid crystal panel substrate using an insulating substrate will now bedescribed.

[0096]FIG. 17 is a cross-sectional view of a configuration of a pixel ina reflective liquid crystal panel substrate. FIG. 17 is across-sectional view along line I-I in the planar layout in FIG. 3, asin FIG. 1. In this embodiment, a TFT is used as a transistor forswitching pixels. In FIG. 17, the sections having the sameidentification numbers as FIGS. 1 and 2 represent the layers and thesemiconductor regions having the same functions as in those drawings.Identification number 1 represents a quartz or non-alkaline glasssubstrate, single-crystal, polycrystalline or amorphous silicon film,regions 5 a, 5 b, 5 c and 8 are formed on the insulating substrate, andinsulating films 4 b and 9 b having a double layer structure composed ofa silicon oxide film formed by thermal oxidation and a silicon nitridefilm formed thereon by a CVD process are formed on the silicon film. AnN-type impurity is doped in the regions 5 a, 5 b and 8 of the siliconfilm before the formation of the upper silicon nitride film among theinsulating film 4 b to form a source region 5 a and a drain region 5 bof the TFT and an electrode region 8 of the holding capacitor. A wiringlayer composed of polysilicon or a metal silicide is formed as a gateelectrode 4 a of the TFT and the other electrode 9 a of the holdingcapacitor is formed on the insulating film 4 b. As described above, theTFT comprising the gate electrode 4 a, the gate insulating film 4 b, thechannel 5 c, the source 5 a and the drain 5 b and the holding capacitorcomprising the electrodes 8 and 9 and the insulating film 9 b areformed.

[0097] A first insulating interlayer 6 composed of silicon nitride orsilicon oxide is formed on the wiring layers 4 a and 9 a, and a sourceelectrode 7 a which is connected to the source region 5 a through acontact hole formed in the insulating film 6 is formed of a first metallayer composed of aluminum. A second insulating interlayer 13 having adouble-layer structure composed of a silicon oxide film and a siliconnitride film is formed on the first metal layer. The second insulatinginterlayer 13 is planarized by a CMP process and a pixel electrode 14,as a reflection electrode, composed of aluminum is formed thereoncorresponding to each pixel. The electrode region 8 of the silicon filmis electrically connected to the pixel electrode 14 through a contacthole 16. Such a connection is achieved by embedding a connecting plug 15composed of a high melting point metal, such as tungsten, as in FIG. 1.

[0098] As described above, since the reflecting electrode is formedabove the TFT and holding capacitor formed on the insulating substrate,the pixel electrode region is expanded and the holding capacitor has alarge area below the reflecting electrode as in the planar layout inFIG. 3. A high aperture ratio (high reflectance) therefore can beachieved even in a high definition panel (having smaller pixels) and anapplied voltage can be sufficiently retained in each pixel, resulting instable driving.

[0099] A passivation film 17 composed of a silicon oxide film is formedon the reflecting electrode 14, as in the above-mentioned embodiments.The thickness of the passivation film 17 is similar to that in thoseembodiments, and a reflective liquid crystal panel substrate having asmall variation of reflectance with the wavelength of the incident lightcan be obtained. A comprehensive configuration of the liquid crystalpanel substrate and a configuration of the liquid crystal panel aresimilar to those in FIGS. 6 and 7.

[0100] In FIG. 17, no insulating interlayer 11 and light shielding layer12 are provided unlike FIG. 1. These layers can also be provided as inFIG. 1 in order to prevent leakage of the incident light from the gap tothe adjacent pixel on the TFT. If incident light from the bottom of thesubstrate is anticipated, a light shielding layer may be provided underthe silicon films 5 a, 5 b and 8. Although the drawing includes a topgate type in which the gate electrode is provided above the channel, abottom gate type in which a gate electrode is previously formed and asilicon film as a channel is provided thereon through a gate insulatingfilm is also available. Also a double layer structure composed of asilicon oxide film and a silicon nitride film in the peripheral circuitregion as in FIG. 4 can improve moisture resistance.

[0101]FIG. 9 shows an example of electronic devices using the liquidcrystal panels in accordance with the present invention, and is a planarschematic diagram of the main section of a projector (projection displaydevice) using a reflective liquid crystal panel in accordance with thepresent invention as a light valve. FIG. 9 is a cross-sectional view ofan XZ plane which passes through the center of an optical element 130.This projector includes a light source 110 provided along the systemlight axis L (111 represents a lamp and 112 represents a reflector), anintegrated lens 120, a polarizing device 130, a polarizing illuminator100 including the polarizing device 130, a polarized beam splitter 200which reflects a S-polarized light beam emerging from the polarizingilluminator 100 by a S-polarized light beam reflecting face 201, adichroic mirror 412 which separates the blue (B) light component fromthe light reflected on the S-polarized light beam reflecting face 201 ofthe polarized beam splitter 200, a reflective liquid crystal light valve300B modulating the separated blue (B) light, a dichroic mirror 413which separates a red (R) light component from the light beam notcontaining the blue light component, a reflective liquid crystal lightvalve 300R modulating the separated red (R) light, a reflective liquidcrystal light valve 300G modulating the residual green (G) light passedthrough the dichroic mirror 413, and a projection optical system 500which includes a projection lens projecting a synthesized light on ascreen 600 in which the modulated light beams from the three reflectionliquid crystal light valves 300R, 300G, and 300B are combined throughthe dichroic mirrors 412 and 413 and the polarized beam splitter 200.These three reflective liquid crystal valves 300R, 300G and 300B areprovided with the above-mentioned liquid crystal panels, respectively.

[0102] The random polarized light beams emerging from the light source110 are divided into a plurality of intermediate light beams by theintegrated lens 120, converted to single-polarization light beams(S-polarized light beam) substantially having a polarized lightdirection with the polarizing device 130 which has a second integratedlens at the light incident side, and are incident on the polarized beamsplitter 200. The S-polarized light beams emerging from the polarizingdevice 130 are reflected from the S-polarized light beam reflecting face201 of the polarized beam splitter 200, the blue (B) light beam amongthe reflected light beams is reflected on the blue light reflectinglayer of the dichroic mirror 412 and modulated by the reflection liquidcrystal light valve 300B. The red (R) light beam among the light beamspassed through the blue light reflecting layer of the dichroic mirror412 is reflected on the red light reflecting layer of the dichroicmirror 413 and modulated by the reflective liquid crystal light valve300R.

[0103] Further, the green (G) light beam passed through the red lightreflecting layer of the dichroic mirror 413 is modulated by thereflective liquid crystal light valve 300G. In such a manner, the colorlight beams modulated by the reflective liquid crystal light valves300R, 300G and 300B are combined by the dichroic mirrors 412 and 413 andthe polarized beam splitter 200, and the combined light is projectedthrough the projection optical system 500.

[0104] The reflective liquid crystal panel used in the reflective liquidcrystal light valves 300R, 300G and 300B contains a TN liquid crystal(longitudinal axes of liquid crystal molecules are substantially alignedin the direction parallel to the panel substrate when no voltage isapplied) or a SH liquid crystal (longitudinal axes of liquid crystalmolecules are substantially aligned in the direction perpendicular tothe panel substrate when no voltage is applied).

[0105] When a TN liquid crystal is used, in a pixel (OFF pixel) in whicha voltage applied to the liquid crystal layer intervened between thereflecting electrode of the pixel and the common electrode of theopposing substrate is lower than a threshold voltage, the incident colorlight is elliptically polarized in the liquid crystal layer, isreflected from the reflecting electrode and emerges from the liquidcrystal layer in which the polarization axis of the emerging light isshifted by 90 degrees from the incident light and ellipticallypolarized. On the other hand, in a pixel (ON pixel) in which a voltageis applied to the liquid crystal layer, the incident color light reachesthe reflective electrode without polarization, is reflected and emerged,in which the emerging light has the same polarization axis as theincident light. Since the alignment angle of the liquid crystal moleculeof the TN liquid crystal varies in response to the voltage applied tothe reflective electrode, the angle of the polarization axis of thereflected light in relation to the incident light varies in response tothe voltage applied to the reflective electrode through the transistorin the pixel.

[0106] When a SH liquid crystal is used, in a pixel (OFF pixel) in whichthe voltage applied to the liquid crystal layer is lower than athreshold voltage, the incident color light reaches the reflectiveelectrode without polarization, is reflected and emerges, in which theemerging light has the same polarization axis as the incident light. Onthe other hand, in a pixel (ON pixel) in which a voltage is applied tothe liquid crystal layer, the incident color light is ellipticallypolarized in the liquid crystal layer, reflected on the reflectiveelectrode and emerges from the liquid crystal layer in which thepolarization axis of the emerging light is shifted by 90 degrees fromthe incident light and the emerging light is elliptically polarized.Since the alignment angle of the liquid crystal molecules of the SHliquid crystal varies in response to the voltage applied to thereflective electrode as in the TN liquid crystal, the angle of thepolarization axis of the reflected light in relation to the incidentlight varies in response to the voltage applied to the reflectiveelectrode through the transistor in the pixel.

[0107] Among the color light beams reflected from pixels in these liquidcrystal panels, the S-polarized light component does not pass throughthe polarized beam splitter 200 which reflects the S-polarized light andtransmits P-polarized light. The light beams passed through thepolarized beam splitter 200 form an image. The projected image is anormally-white display when a TN liquid crystal is used in the liquidcrystal panel because the reflected light beams in OFF pixels reach theprojection optical system 500 and the reflected light beams in ON pixelsdo not reach the lens, and a normally-black display when a SH liquidcrystal is used because the reflected light beams in OFF pixels do notreach the projection optical system and the reflected light beams in ONpixels reach the projection optical system 500.

[0108] Since reflective liquid crystal panels permit larger pixelelectrodes compared to transmission active matrix liquid crystal panels,high reflectance is achieved, high density images can be projected athigh contrast and projectors can be miniaturized.

[0109] As shown in FIG. 7, the peripheral circuit section of the liquidcrystal panel is covered with the light shielding film, and the samevoltage (for example, the LC common voltage; if the LC common voltage isnot used, the peripheral counter electrode is separated from the counterelectrode in the pixel) is applied to the section and the counterelectrode formed at the position in which the opposing substrate isopposed. Almost zero volts is therefore applied to the liquid crystalintervened between them and the liquid crystal is the same as an OFFstate. As a result, in the TN liquid crystal panel the periphery of theimage region exhibits an entire white display in response to thenormally-white display, whereas in the SH liquid crystal panel theperiphery of the image region exhibits an entire black display inresponse to the normally-black display.

[0110] Further satisfactory results are obtained when the silicon oxideforming the passivation film of the light valve 300R as the firstreflective liquid crystal panel modulating red light separated by thepolarized beam splitter 200 as a color separation means which separatesthe light from the light source 110 into three primaries has a thicknessin a range of 1,300 to 1,900 angstroms, the silicon oxide forming thepassivation film of the light valve 300G as the second reflective liquidcrystal panel modulating green light has a thickness in a range of 1,200to 1,600 angstroms, and the silicon oxide forming the passivation filmof the light valve 300B as the third reflective liquid crystal panelmodulating blue light has a thickness in a range of 900 to 1,200angstroms.

[0111] In accordance with the above-mentioned embodiment, a voltageapplied to each of pixels in the reflective liquid crystal panels 300R,300G and 300B is sufficiently retained and the pixel electrode has asignificantly high reflectance, resulting in clear projected images.

[0112]FIG. 15 includes views illustrating appearances of electronicdevices using the reflection liquid crystal panels in accordance withthe present invention. In these electronic devices, the reflectionliquid crystal panel is used as a direct viewing-type reflection liquidcrystal panel, not as a light valve which is used together with apolarized beam splitter. The reflecting electrode must therefore not bea perfect mirror surface and preferably has adequate unevenness. Otherconfigurations are basically the same as the light valve.

[0113]FIG. 15(a) is an isometric view of a portable telephone.Identification number 1000 represents a portable telephone main body,and identification number 1001 represents a liquid crystal display usinga reflective liquid crystal panel in accordance with the presentinvention.

[0114]FIG. 15(b) shows a watch-type electronic device. Identificationnumber 1100 is an isometric view of a watch main body. Identificationnumber 1101 represents a liquid crystal display using a reflectiveliquid crystal panel in accordance with the present invention. Since theliquid crystal panel has high definition pixels compared to conventionalwatch displays and is capable of displaying television images, awatch-type television can be achieved.

[0115]FIG. 15(c) shows a portable information processing unit, e.g. aword processor or a personal computer. Identification number 1200represents an information processing unit, identification number 1202represents an input section such as a keyboard, identification number1206 represents a display using a reflective liquid crystal panel inaccordance with the present invention, and identification number 1204represents an information processing unit main body. Since theseelectronic devices are driven by batteries, the use of the reflectiveliquid crystal panel having no light source lamp can lengthen thebattery life. Since the peripheral circuits can be stored in the panelsubstrate, significant reduction of parts, and weight and size reductioncan be achieved.

[0116] In the above-mentioned embodiments, although a TN type and ahomeotropic alignment SH type are exemplified as a liquid crystal of theliquid crystal panel, other types of liquid crystals are also available.

[0117] As described above, a reflective liquid crystal panel substratein accordance with the present invention is provided with a passivationfilm, and thus has improved reliability. The use of a silicon oxide filmhaving a thickness of 500 to 2,000 angstroms as the passivation reducesdependence of reflectance of the pixel electrode on variation of thethickness. In particular, the silicon oxide film having a thickness of500 to 2,000 angstroms exhibits slight dependence of the reflectance onthe wavelength and thus can reduce variation of the reflectance.

[0118] The thickness of the silicon oxide film as the passivation filmis set to an adequate range in response to the wavelength of theincident light, e.g. 900 to 1,200 angstroms for a pixel electrodereflecting blue light, 1,200 to 1,600 angstroms for a pixel electrodereflecting green light, and 1,300 to 1,900 angstroms for a pixelelectrode reflecting red light. Variation of the reflectance in eachcolor can therefore be suppressed to 1% or less. As a result,reliability of the liquid crystal panel can be improved, and the imagequality of a projection display device using the reflective liquidcrystal panel as a light valve can be improved.

[0119] Since the thickness of the silicon oxide film as the passivationfilm is determined in response to the thickness of the alignment filmformed thereon and the thickness of the alignment film is set to a rangeof 300 to 1,400 angstroms, variation of the refractive index of theliquid crystal can be effectively prevented.

[0120] In a reflective liquid crystal panel in which a pixel regioncomprising a matrix of pixel electrodes and peripheral circuits, such asa shift register and a control circuit, provided outside the pixelregion are formed on the same substrate, a passivation film composed ofa silicon oxide film is formed above the pixel region and a passivationfilm composed of a silicon nitride film is formed above the peripheralcircuits. The use of the silicon nitride film above the peripheralcircuits further secures protection of the peripheral circuits andimproves reliability.

[0121] A silicon nitride film is provided as an insulating interlayerbetween the reflective electrode and a metal layer thereunder instead ofthe passivation film above the reflective electrode or together with thepassivation film composed of the silicon oxide film. The moistureresistance is therefore improved, a MOSFET for pixel switching and aholding capacitor can be prevented from corrosion due to water or thelike.

[0122] A monolithic protective structure in which a silicon nitride filmis formed on a passivation film composed of a silicon oxide film isprovided over the edge and side wall of a laminate of an insulatinginterlayer formed at the periphery of the pixel region and a metal layershielding the periphery. The waterproof property at the edge of theliquid crystal panel in which water readily penetrates is thereforeimproved and durability is also improved due to its reinforcementeffect.

What is claimed is:
 1. A liquid crystal panel substrate comprising:reflecting electrodes formed on a substrate; a switching element formedcorresponding to each of the reflecting electrodes; a passivation filmformed on said reflecting electrodes comprising a silicon oxide film;and a silicon nitride film formed as an insulating interlayer betweensaid reflecting electrodes and a metal layer thereunder having moistureresistance.
 2. A liquid crystal panel substrate according to claim 1,wherein said insulating interlayer between said reflecting electrodesand said metal layer thereunder comprises a silicon nitride film and asilicon oxide film, and has a laminate structure in which said siliconnitride film is formed on said silicon oxide film.
 3. A liquid crystalpanel substrate comprising: a pixel region having a matrix of reflectingelectrodes formed on a substrate and a switching element formedcorresponding to each of said reflecting electrodes, a periphery regionof said pixel region on the substrate having a metal layer and aninsulating interlayer; and a passivation film having a laminatestructure comprising a silicon oxide film and a silicon nitride film onsaid silicon oxide film, the passivation film being formed at edgesections of the metal layer and the insulating interlayer.
 4. A liquidcrystal panel substrate comprising: a pixel region having a matrix ofreflecting electrodes formed on a substrate and a transistor formedcorresponding to each of the reflecting electrodes; a peripheral circuitarranged in a periphery region of said pixel region on the substrate forsupplying signals to said transistors in said pixel region; a firstpassivation film comprising a silicon oxide film formed on saidreflecting electrodes in said pixel region; and a second passivationfilm comprising a silicon nitride film formed on said periphery region.5. A liquid crystal panel substrate according to claim 4, the siliconnitride film being a first silicon nitride film, the liquid crystalpanel substrate further comprising a second silicon nitride film as aninsulating interlayer provided between said reflecting electrodes and ametal layer thereunder.
 6. A liquid crystal panel substrate according toclaim 5, the silicon oxide film being a first silicon oxide film, saidinsulating interlayer between said reflecting electrodes and said metallayer thereunder comprising the second silicon nitride film and a secondsilicon oxide film, and having a laminate structure in which said secondsilicon nitride film is formed on said second silicon oxide film.
 7. Aliquid crystal panel substrate comprising: a pixel region having amatrix of reflecting electrodes formed on a substrate and transistorformed corresponding to each of the reflecting electrodes; a peripheralcircuit arranged in a periphery region of said pixel region on thesubstrate for supplying signals to said transistors in said pixelregion, the periphery region having a metal layer and an insulatinglayer; a first passivation film comprising a first silicon oxide filmformed in said pixel region; and a second passivation film having alaminate structure comprising a second silicon oxide film and a siliconnitride film formed on the second silicon oxide film, the secondpassivation film being formed at edge sections of the metal layer andthe insulating interlayer.
 8. A liquid crystal panel substrate accordingto claim 3, further comprising a seal material formed on said siliconnitride film for sealing with a counter substrate.
 9. A liquid crystalpanel substrate according to claim 3, said edge section of said metallayer and the insulating interlayer being a scribed region of thesubstrate.
 10. A liquid crystal panel substrate comprising: a pixelregion having reflecting electrodes formed on a semiconductor substrateand a switching element formed corresponding to each of the reflectingelectrodes; and a passivation film formed by a silicon nitride filmhaving moisture resistance and formed on a scribed region of saidsemiconductor substrate.
 11. A liquid crystal panel substrate accordingto claim 10, said passivation film having a laminate structurecomprising a silicon oxide film and the silicon nitride film formed onthe silicon oxide film.
 12. A liquid crystal panel comprising a firstsubstrate, a second substrate opposed to the first substrate, a liquidcrystal therebetween, and a seal material sealing the first substrateand the second substrate, the liquid crystal panel further comprising: apixel region having reflecting electrodes formed on said firstsubstrate; and a passivation film comprising a silicon nitride filmformed in a region arranged with said seal material on said firstsubstrate, the seal material being formed on the silicon nitride.
 13. Aliquid crystal panel according to claim 12, the passivation film being afirst passivation film and the liquid crystal panel further comprising asecond passivation film comprising a silicon oxide film formed on thereflecting electrodes.